Fundamentals of vertical density profile formation in wood composites. Part I. In-situ density measurement of the consolidation process

We have designed a radiation-based system for measuring density of wood com posite mats during consolidation. The system is installed on a laboratory h ot-press and has been used to study consolidation of medium density fiberbo ard (MDF) and oriented strandboard (OSB) mars. Measuring density of the woo d mat during consolidation is a key parameter for understanding subsequent product performance. The in-situ measuring system provides for density meas urement at three horizontal planes in the wood mat, at positions of 25%, 50 %, and 75% of the mat thickness at any time during the press cycle. The sys tem incorporates three cesium(137) sources and electronic detection equipme nt, collimated to move in concert with the up-acting press platen. Radiatio n count data taken through the mat during pressing are converted to density after pressing. Press position and time are simultaneously recorded with t he count data. Moisture migration during hot-pressing resulted in significa nt density changes as measured by the in-press radiation-based system. Clea rly established in all laboratory pressing studies is the indication that t he vertical density profile of wood composite panels is formed from a combi nation of actions that occur both during consolidation and also after the p ress has reached final position; measurements recorded in the press show th at mat densification continues after the press has reached final position. A description of the radiation system and data from elementary pressing exa mples are presented, along with experimental results of the effects of mois ture migration in the mat on measured density during pressing.